/*
 * Copyright (c) 2023, Ali Mohammad Pur <mpfard@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/ByteReader.h>
#include <AK/Debug.h>
#include <AK/FlyString.h>
#include <AK/Random.h>
#include <AK/SourceLocation.h>
#include <AK/Tuple.h>
#include <LibCore/File.h>
#include <LibWasm/AbstractMachine/Interpreter.h>
#include <LibWasm/Printer/Printer.h>
#include <LibWasm/Wasi.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>

namespace Wasm::Wasi::ABI {

template<typename T>
Wasm::Value CompatibleValue<T>::to_wasm_value() const
{
    return Wasm::Value(value);
}

template<typename T>
T deserialize(CompatibleValue<T> const& data)
{
    return deserialize<T>(Array { ReadonlyBytes { &data.value, sizeof(data.value) } });
}

template<typename T, size_t N>
void serialize(T const& value, Array<Bytes, N> bytes)
{
    if constexpr (IsEnum<T>)
        return serialize(to_underlying(value), move(bytes));
    else if constexpr (IsIntegral<T>)
        ReadonlyBytes { &value, sizeof(value) }.copy_to(bytes[0]);
    else if constexpr (IsSpecializationOf<T, DistinctNumeric>)
        return serialize(value.value(), move(bytes));
    else
        return value.serialize_into(move(bytes));
}

template<typename T, size_t N>
T deserialize(Array<ReadonlyBytes, N> const& bytes)
{
    if constexpr (IsEnum<T>) {
        return static_cast<T>(deserialize<UnderlyingType<T>>(bytes));
    } else if constexpr (IsIntegral<T>) {
        T value;
        ByteReader::load(bytes[0].data(), value);
        return value;
    } else if constexpr (IsSpecializationOf<T, DistinctNumeric>) {
        return deserialize<RemoveCVReference<decltype(T(0).value())>>(bytes);
    } else {
        return T::read_from(bytes);
    }
}

template<typename T>
CompatibleValue<T> to_compatible_value(Wasm::Value const& value)
{
    using Type = typename ToCompatibleValue<T>::Type;
    // Note: the type can't be something else, we've already checked before through the function type's runtime checker.
    auto converted_value = value.template to<Type>();
    return { .value = converted_value };
}

}

namespace Wasm::Wasi {

void ArgsSizes::serialize_into(Array<Bytes, 2> bytes) const
{
    ABI::serialize(count, Array { bytes[0] });
    ABI::serialize(size, Array { bytes[1] });
}

void EnvironSizes::serialize_into(Array<Bytes, 2> bytes) const
{
    ABI::serialize(count, Array { bytes[0] });
    ABI::serialize(size, Array { bytes[1] });
}

void SockRecvResult::serialize_into(Array<Bytes, 2> bytes) const
{
    ABI::serialize(size, Array { bytes[0] });
    ABI::serialize(roflags, Array { bytes[1] });
}

void ROFlags::serialize_into(Array<Bytes, 1> bytes) const
{
    ABI::serialize(data, Array { bytes[0] });
}

template<typename T>
void LittleEndian<T>::serialize_into(Array<Bytes, 1> bytes) const
{
    ABI::serialize(m_value, move(bytes));
}

template<typename T>
LittleEndian<T> LittleEndian<T>::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    auto swapped = ABI::deserialize<T>(bytes);
    return bit_cast<LittleEndian<T>>(swapped);
}

Rights Rights::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    Rights rights { .data = 0 };
    bytes[0].copy_to(rights.data.bytes());
    return rights;
}

void Rights::serialize_into(Array<Bytes, 1> bytes) const
{
    data.bytes().copy_to(bytes[0]);
}

void FDFlags::serialize_into(Array<Bytes, 1> bytes) const
{
    ReadonlyBytes { &data, sizeof(data) }.copy_to(bytes[0]);
}

FDFlags FDFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    FDFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

FSTFlags FSTFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    FSTFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

OFlags OFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    OFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

SDFlags SDFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    SDFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

void FDStat::serialize_into(Array<Bytes, 1> bytes) const
{
    auto data = bytes[0];
    ABI::serialize(fs_filetype, Array { data.slice(offsetof(FDStat, fs_filetype), sizeof(fs_filetype)) });
    ABI::serialize(fs_flags, Array { data.slice(offsetof(FDStat, fs_flags), sizeof(fs_flags)) });
    ABI::serialize(fs_rights_base, Array { data.slice(offsetof(FDStat, fs_rights_base), sizeof(fs_rights_base)) });
    ABI::serialize(fs_rights_inheriting, Array { data.slice(offsetof(FDStat, fs_rights_inheriting), sizeof(fs_rights_inheriting)) });
}

void PreStat::serialize_into(Array<Bytes, 1> bytes) const
{
    auto data = bytes[0];
    ABI::serialize(type, Array { data.slice(0, sizeof(type)) });
    if (type == PreOpenType::Dir)
        ABI::serialize(dir, Array { data.slice(offsetof(PreStat, dir), sizeof(dir)) });
    else
        VERIFY_NOT_REACHED();
}

void PreStatDir::serialize_into(Array<Bytes, 1> bytes) const
{
    ABI::serialize(pr_name_len, move(bytes));
}

void FileStat::serialize_into(Array<Bytes, 1> bytes) const
{
    auto data = bytes[0];
    ABI::serialize(dev, Array { data.slice(0, sizeof(dev)) });
    ABI::serialize(ino, Array { data.slice(offsetof(FileStat, ino), sizeof(ino)) });
    ABI::serialize(filetype, Array { data.slice(offsetof(FileStat, filetype), sizeof(filetype)) });
    ABI::serialize(nlink, Array { data.slice(offsetof(FileStat, nlink), sizeof(nlink)) });
    ABI::serialize(size, Array { data.slice(offsetof(FileStat, size), sizeof(size)) });
    ABI::serialize(atim, Array { data.slice(offsetof(FileStat, atim), sizeof(atim)) });
    ABI::serialize(mtim, Array { data.slice(offsetof(FileStat, mtim), sizeof(mtim)) });
    ABI::serialize(ctim, Array { data.slice(offsetof(FileStat, ctim), sizeof(ctim)) });
}

RIFlags RIFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    RIFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

LookupFlags LookupFlags::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    LookupFlags flags { .data = 0 };
    bytes[0].copy_to(flags.data.bytes());
    return flags;
}

CIOVec CIOVec::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    return CIOVec {
        .buf = ABI::deserialize<decltype(buf)>(Array { bytes[0].slice(offsetof(CIOVec, buf), sizeof(buf)) }),
        .buf_len = ABI::deserialize<decltype(buf_len)>(Array { bytes[0].slice(offsetof(CIOVec, buf_len), sizeof(buf_len)) }),
    };
}

IOVec IOVec::read_from(Array<ReadonlyBytes, 1> const& bytes)
{
    return IOVec {
        .buf = ABI::deserialize<decltype(buf)>(Array { bytes[0].slice(offsetof(IOVec, buf), sizeof(buf)) }),
        .buf_len = ABI::deserialize<decltype(buf_len)>(Array { bytes[0].slice(offsetof(IOVec, buf_len), sizeof(buf_len)) }),
    };
}

template<typename T>
ErrorOr<Vector<T>> copy_typed_array(Configuration& configuration, Pointer<T> source, Size count)
{
    Vector<T> values;
    TRY(values.try_ensure_capacity(count));
    auto* memory = configuration.store().get(MemoryAddress { 0 });
    if (!memory)
        return Error::from_errno(ENOMEM);

    UnderlyingPointerType address = source.value();
    auto size = sizeof(T);
    if (memory->size() < address || memory->size() <= address + (size * count)) {
        return Error::from_errno(ENOBUFS);
    }

    for (Size i = 0; i < count; i += 1) {
        values.unchecked_append(T::read_from(Array { ReadonlyBytes { memory->data().bytes().slice(address, size) } }));
        address += size;
    }

    return values;
}

template<typename T>
ErrorOr<void> copy_typed_value_to(Configuration& configuration, T const& value, Pointer<T> destination)
{
    auto* memory = configuration.store().get(MemoryAddress { 0 });
    if (!memory)
        return Error::from_errno(ENOMEM);

    UnderlyingPointerType address = destination.value();
    auto size = sizeof(T);
    if (memory->size() < address || memory->size() <= address + size) {
        return Error::from_errno(ENOBUFS);
    }

    ABI::serialize(value, Array { Bytes { memory->data().bytes().slice(address, size) } });
    return {};
}

template<typename T>
ErrorOr<Span<T>> slice_typed_memory(Configuration& configuration, Pointer<T> source, Size count)
{
    auto* memory = configuration.store().get(MemoryAddress { 0 });
    if (!memory)
        return Error::from_errno(ENOMEM);

    auto address = source.value();
    auto size = sizeof(T);
    if (memory->size() < address || memory->size() <= address + (size * count))
        return Error::from_errno(ENOBUFS);

    auto untyped_slice = memory->data().bytes().slice(address, size * count);
    return Span<T>(untyped_slice.data(), count);
}

template<typename T>
ErrorOr<Span<T const>> slice_typed_memory(Configuration& configuration, ConstPointer<T> source, Size count)
{
    auto* memory = configuration.store().get(MemoryAddress { 0 });
    if (!memory)
        return Error::from_errno(ENOMEM);

    auto address = source.value();
    auto size = sizeof(T);
    if (memory->size() < address || memory->size() <= address + (size * count))
        return Error::from_errno(ENOBUFS);

    auto untyped_slice = memory->data().bytes().slice(address, size * count);
    return Span<T const>(untyped_slice.data(), count);
}

static ErrorOr<size_t> copy_string_including_terminating_null(Configuration& configuration, StringView string, Pointer<u8> target)
{
    auto slice = TRY(slice_typed_memory(configuration, target, string.bytes().size() + 1));
    string.bytes().copy_to(slice);
    slice[string.bytes().size()] = 0;
    return slice.size();
}

static ErrorOr<size_t> copy_string_excluding_terminating_null(Configuration& configuration, StringView string, Pointer<u8> target, Size target_length)
{
    auto byte_count = min(string.bytes().size(), target_length);
    auto slice = TRY(slice_typed_memory(configuration, target, byte_count));
    string.bytes().copy_trimmed_to(slice);
    return byte_count;
}

static Errno errno_value_from_errno(int value);
static FileType file_type_of(struct stat const& buf);
static FDFlags fd_flags_of(struct stat const& buf);

Vector<AK::String> const& Implementation::arguments() const
{
    if (!cache.cached_arguments.has_value()) {
        cache.cached_arguments.lazy_emplace([&] {
            if (provide_arguments)
                return provide_arguments();
            return Vector<AK::String> {};
        });
    }

    return *cache.cached_arguments;
}

Vector<AK::String> const& Implementation::environment() const
{
    if (!cache.cached_environment.has_value()) {
        cache.cached_environment.lazy_emplace([&] {
            if (provide_environment)
                return provide_environment();
            return Vector<AK::String> {};
        });
    }

    return *cache.cached_environment;
}

Vector<Implementation::MappedPath> const& Implementation::preopened_directories() const
{
    if (!cache.cached_preopened_directories.has_value()) {
        cache.cached_preopened_directories.lazy_emplace([&] {
            if (provide_preopened_directories)
                return provide_preopened_directories();
            return Vector<MappedPath> {};
        });
    }

    return *cache.cached_preopened_directories;
}

Implementation::Descriptor Implementation::map_fd(FD fd)
{
    u32 fd_value = fd.value();
    if (auto* value = m_fd_map.find(fd_value))
        return value->downcast<Descriptor>();

    return UnmappedDescriptor(fd_value);
}

ErrorOr<Result<void>> Implementation::impl$args_get(Configuration& configuration, Pointer<Pointer<u8>> argv, Pointer<u8> argv_buf)
{
    UnderlyingPointerType raw_argv_buffer = argv_buf.value();
    UnderlyingPointerType raw_argv = argv.value();

    for (auto& entry : arguments()) {
        auto ptr = Pointer<u8> { raw_argv_buffer };
        auto byte_count = TRY(copy_string_including_terminating_null(configuration, entry.bytes_as_string_view(), ptr));
        raw_argv_buffer += byte_count;

        TRY(copy_typed_value_to(configuration, ptr, Pointer<Pointer<u8>> { raw_argv }));
        raw_argv += sizeof(ptr);
    }

    return Result<void> {};
}

ErrorOr<Result<ArgsSizes>> Implementation::impl$args_sizes_get(Configuration&)
{
    size_t count = 0;
    size_t total_size = 0;
    for (auto& entry : arguments()) {
        count += 1;
        total_size += entry.bytes().size() + 1; // 1 extra byte for terminating null.
    }

    return Result<ArgsSizes>(ArgsSizes {
        count,
        total_size,
    });
}

ErrorOr<Result<void>> Implementation::impl$environ_get(Configuration& configuration, Pointer<Pointer<u8>> environ, Pointer<u8> environ_buf)
{
    UnderlyingPointerType raw_environ_buffer = environ_buf.value();
    UnderlyingPointerType raw_environ = environ.value();

    for (auto& entry : environment()) {
        auto ptr = Pointer<u8> { raw_environ_buffer };
        auto byte_count = TRY(copy_string_including_terminating_null(configuration, entry.bytes_as_string_view(), ptr));
        raw_environ_buffer += byte_count;

        TRY(copy_typed_value_to(configuration, ptr, Pointer<Pointer<u8>> { raw_environ }));
        raw_environ += sizeof(ptr);
    }

    return Result<void> {};
}

ErrorOr<Result<EnvironSizes>> Implementation::impl$environ_sizes_get(Configuration&)
{
    size_t count = 0;
    size_t total_size = 0;
    for (auto& entry : environment()) {
        count += 1;
        total_size += entry.bytes().size() + 1; // 1 extra byte for terminating null.
    }

    return Result<EnvironSizes>(EnvironSizes {
        count,
        total_size,
    });
}

ErrorOr<void> Implementation::impl$proc_exit(Configuration&, ExitCode exit_code)
{
    return Error::from_errno(-static_cast<i32>(exit_code + 1));
}

ErrorOr<Result<void>> Implementation::impl$fd_close(Configuration&, FD fd)
{
    return map_fd(fd).visit(
        [&](u32 fd) -> Result<void> {
            if (close(bit_cast<i32>(fd)) != 0)
                return errno_value_from_errno(errno);
            return {};
        },
        [&](PreopenedDirectoryDescriptor) -> Result<void> {
            return errno_value_from_errno(EISDIR);
        },
        [&](UnmappedDescriptor) -> Result<void> {
            return errno_value_from_errno(EBADF);
        });
}

ErrorOr<Result<Size>> Implementation::impl$fd_write(Configuration& configuration, FD fd, Pointer<CIOVec> iovs, Size iovs_len)
{
    auto mapped_fd = map_fd(fd);
    if (!mapped_fd.has<u32>())
        return errno_value_from_errno(EBADF);

    u32 fd_value = mapped_fd.get<u32>();
    Size bytes_written = 0;
    for (auto& iovec : TRY(copy_typed_array(configuration, iovs, iovs_len))) {
        auto slice = TRY(slice_typed_memory(configuration, iovec.buf, iovec.buf_len));
        auto result = write(fd_value, slice.data(), slice.size());
        if (result < 0)
            return errno_value_from_errno(errno);
        bytes_written += static_cast<Size>(result);
    }
    return bytes_written;
}

ErrorOr<Result<PreStat>> Implementation::impl$fd_prestat_get(Configuration&, FD fd)
{
    auto& paths = preopened_directories();
    return map_fd(fd).visit(
        [&](UnmappedDescriptor unmapped_fd) -> Result<PreStat> {
            // Map the new fd to the next available directory.
            if (m_first_unmapped_preopened_directory_index >= paths.size())
                return errno_value_from_errno(EBADF);

            auto index = m_first_unmapped_preopened_directory_index++;
            m_fd_map.insert(unmapped_fd.value(), PreopenedDirectoryDescriptor(index));
            return PreStat {
                .type = PreOpenType::Dir,
                .dir = PreStatDir {
                    .pr_name_len = paths[index].mapped_path.string().bytes().size(),
                },
            };
        },
        [&](u32) -> Result<PreStat> {
            return errno_value_from_errno(EBADF);
        },
        [&](PreopenedDirectoryDescriptor fd) -> Result<PreStat> {
            return PreStat {
                .type = PreOpenType::Dir,
                .dir = PreStatDir {
                    .pr_name_len = paths[fd.value()].mapped_path.string().bytes().size(),
                },
            };
        });
}

ErrorOr<Result<void>> Implementation::impl$fd_prestat_dir_name(Configuration& configuration, FD fd, Pointer<u8> path, Size path_len)
{
    auto mapped_fd = map_fd(fd);
    if (!mapped_fd.has<PreopenedDirectoryDescriptor>())
        return errno_value_from_errno(EBADF);

    auto& entry = preopened_directories()[mapped_fd.get<PreopenedDirectoryDescriptor>().value()];
    auto byte_count = TRY(copy_string_excluding_terminating_null(configuration, entry.mapped_path.string().view(), path, path_len));
    if (byte_count < path_len.value())
        return errno_value_from_errno(ENOBUFS);

    return Result<void> {};
}

ErrorOr<Result<FileStat>> Implementation::impl$path_filestat_get(Configuration& configuration, FD fd, LookupFlags flags, ConstPointer<u8> path, Size path_len)
{
    auto dir_fd = AT_FDCWD;

    auto mapped_fd = map_fd(fd);
    mapped_fd.visit(
        [&](PreopenedDirectoryDescriptor descriptor) {
            auto& entry = preopened_directories()[descriptor.value()];
            dir_fd = entry.opened_fd.value_or_lazy_evaluated([&] {
                ByteString path = entry.host_path.string();
                return open(path.characters(), O_DIRECTORY, 0);
            });
            entry.opened_fd = dir_fd;
        },
        [&](u32 fd) {
            dir_fd = fd;
        },
        [](UnmappedDescriptor) {});

    if (dir_fd < 0 && dir_fd != AT_FDCWD)
        return errno_value_from_errno(errno);

    int options = 0;
    if (!flags.bits.symlink_follow)
        options |= AT_SYMLINK_NOFOLLOW;

    auto slice = TRY(slice_typed_memory(configuration, path, path_len));
    auto null_terminated_string = ByteString::copy(slice);

    struct stat stat_buf;
    if (fstatat(dir_fd, null_terminated_string.characters(), &stat_buf, options) < 0)
        return errno_value_from_errno(errno);

    constexpr auto file_type_of = [](struct stat const& buf) {
        if (S_ISDIR(buf.st_mode))
            return FileType::Directory;
        if (S_ISCHR(buf.st_mode))
            return FileType::CharacterDevice;
        if (S_ISBLK(buf.st_mode))
            return FileType::BlockDevice;
        if (S_ISREG(buf.st_mode))
            return FileType::RegularFile;
        if (S_ISFIFO(buf.st_mode))
            return FileType::Unknown; // FIXME: FileType::Pipe is currently not present in WASI (but it should be) so we use Unknown for now.
        if (S_ISLNK(buf.st_mode))
            return FileType::SymbolicLink;
        if (S_ISSOCK(buf.st_mode))
            return FileType::SocketStream;
        return FileType::Unknown;
    };

    return Result(FileStat {
        .dev = stat_buf.st_dev,
        .ino = stat_buf.st_ino,
        .filetype = file_type_of(stat_buf),
        .nlink = stat_buf.st_nlink,
        .size = stat_buf.st_size,
        .atim = stat_buf.st_atime,
        .mtim = stat_buf.st_mtime,
        .ctim = stat_buf.st_ctime,
    });
}

ErrorOr<Result<void>> Implementation::impl$path_create_directory(Configuration& configuration, FD fd, Pointer<u8> path, Size path_len)
{
    auto dir_fd = AT_FDCWD;

    auto mapped_fd = map_fd(fd);
    mapped_fd.visit(
        [&](PreopenedDirectoryDescriptor descriptor) {
            auto& entry = preopened_directories()[descriptor.value()];
            dir_fd = entry.opened_fd.value_or_lazy_evaluated([&] {
                ByteString path = entry.host_path.string();
                return open(path.characters(), O_DIRECTORY, 0);
            });
            entry.opened_fd = dir_fd;
        },
        [&](u32 fd) {
            dir_fd = fd;
        },
        [](UnmappedDescriptor) {});

    if (dir_fd < 0 && dir_fd != AT_FDCWD)
        return errno_value_from_errno(errno);

    auto slice = TRY(slice_typed_memory(configuration, path, path_len));
    auto null_terminated_string = ByteString::copy(slice);

    if (mkdirat(dir_fd, null_terminated_string.characters(), 0755) < 0)
        return errno_value_from_errno(errno);

    return Result<void> {};
}

ErrorOr<Result<FD>> Implementation::impl$path_open(Configuration& configuration, FD fd, LookupFlags lookup_flags, Pointer<u8> path, Size path_len, OFlags o_flags, Rights, Rights, FDFlags fd_flags)
{
    auto dir_fd = AT_FDCWD;

    auto mapped_fd = map_fd(fd);
    mapped_fd.visit(
        [&](PreopenedDirectoryDescriptor descriptor) {
            auto& entry = preopened_directories()[descriptor.value()];
            dir_fd = entry.opened_fd.value_or_lazy_evaluated([&] {
                ByteString path = entry.host_path.string();
                return open(path.characters(), O_DIRECTORY, 0);
            });
            entry.opened_fd = dir_fd;
        },
        [&](u32 fd) {
            dir_fd = fd;
        },
        [](UnmappedDescriptor) {});

    if (dir_fd < 0 && dir_fd != AT_FDCWD)
        return errno_value_from_errno(errno);

    // FIXME: What should we do with dsync/rsync?

    int open_flags = 0;
    if (fd_flags.bits.append)
        open_flags |= O_APPEND;
    if (fd_flags.bits.nonblock)
        open_flags |= O_NONBLOCK;
    if (fd_flags.bits.sync)
        open_flags |= O_SYNC;

    if (o_flags.bits.trunc)
        open_flags |= O_TRUNC;
    if (o_flags.bits.creat)
        open_flags |= O_CREAT;
    if (o_flags.bits.directory)
        open_flags |= O_DIRECTORY;
    if (o_flags.bits.excl)
        open_flags |= O_EXCL;

    if (!lookup_flags.bits.symlink_follow)
        open_flags |= O_NOFOLLOW;

    auto path_data = TRY(slice_typed_memory(configuration, path, path_len));
    auto path_string = ByteString::copy(path_data);

    dbgln_if(WASI_FINE_GRAINED_DEBUG, "path_open: dir_fd={}, path={}, open_flags={}", dir_fd, path_string, open_flags);

    int opened_fd = openat(dir_fd, path_string.characters(), open_flags, 0644);
    if (opened_fd < 0)
        return errno_value_from_errno(errno);

    // FIXME: Implement Rights and RightsInheriting.

    m_fd_map.insert(opened_fd, static_cast<u32>(opened_fd));

    return FD(opened_fd);
}

ErrorOr<Result<Timestamp>> Implementation::impl$clock_time_get(Configuration&, ClockID id, Timestamp precision)
{
    constexpr u64 nanoseconds_in_millisecond = 1000'000ull;
    constexpr u64 nanoseconds_in_second = 1000'000'000ull;

    clockid_t clock_id;
    switch (id) {
    case ClockID::Realtime:
        if (precision >= nanoseconds_in_millisecond)
            clock_id = CLOCK_REALTIME_COARSE;
        else
            clock_id = CLOCK_REALTIME;
        break;
    case ClockID::Monotonic:
        if (precision >= nanoseconds_in_millisecond)
            clock_id = CLOCK_MONOTONIC_COARSE;
        else
            clock_id = CLOCK_MONOTONIC;
        break;
    case ClockID::ProcessCPUTimeID:
    case ClockID::ThreadCPUTimeID:
        return Errno::NoSys;
        break;
    }

    struct timespec ts;
    if (clock_gettime(clock_id, &ts) < 0)
        return errno_value_from_errno(errno);

    return Result<Timestamp> { static_cast<u64>(ts.tv_sec) * nanoseconds_in_second + static_cast<u64>(ts.tv_nsec) };
}

ErrorOr<Result<FileStat>> Implementation::impl$fd_filestat_get(Configuration&, FD fd)
{
    int resolved_fd = -1;

    auto mapped_fd = map_fd(fd);
    mapped_fd.visit(
        [&](PreopenedDirectoryDescriptor descriptor) {
            auto& entry = preopened_directories()[descriptor.value()];
            resolved_fd = entry.opened_fd.value_or_lazy_evaluated([&] {
                ByteString path = entry.host_path.string();
                return open(path.characters(), O_DIRECTORY, 0);
            });
            entry.opened_fd = resolved_fd;
        },
        [&](u32 fd) {
            resolved_fd = fd;
        },
        [](UnmappedDescriptor) {});

    if (resolved_fd < 0)
        return errno_value_from_errno(errno);

    struct stat stat_buf;
    if (fstat(resolved_fd, &stat_buf) < 0)
        return errno_value_from_errno(errno);

    constexpr auto file_type_of = [](struct stat const& buf) {
        if (S_ISDIR(buf.st_mode))
            return FileType::Directory;
        if (S_ISCHR(buf.st_mode))
            return FileType::CharacterDevice;
        if (S_ISBLK(buf.st_mode))
            return FileType::BlockDevice;
        if (S_ISREG(buf.st_mode))
            return FileType::RegularFile;
        if (S_ISFIFO(buf.st_mode))
            return FileType::Unknown; // no Pipe? :yakfused:
        if (S_ISLNK(buf.st_mode))
            return FileType::SymbolicLink;
        if (S_ISSOCK(buf.st_mode))
            return FileType::SocketDGram; // :shrug:
        return FileType::Unknown;
    };

    return Result(FileStat {
        .dev = stat_buf.st_dev,
        .ino = stat_buf.st_ino,
        .filetype = file_type_of(stat_buf),
        .nlink = stat_buf.st_nlink,
        .size = stat_buf.st_size,
        .atim = stat_buf.st_atime,
        .mtim = stat_buf.st_mtime,
        .ctim = stat_buf.st_ctime,
    });
}

ErrorOr<Result<void>> Implementation::impl$random_get(Configuration& configuration, Pointer<u8> buf, Size buf_len)
{
    auto buffer_slice = TRY(slice_typed_memory(configuration, buf, buf_len));
    fill_with_random(buffer_slice);

    return Result<void> {};
}

ErrorOr<Result<Size>> Implementation::impl$fd_read(Configuration& configuration, FD fd, Pointer<IOVec> iovs, Size iovs_len)
{
    auto mapped_fd = map_fd(fd);
    if (!mapped_fd.has<u32>())
        return errno_value_from_errno(EBADF);

    u32 fd_value = mapped_fd.get<u32>();
    Size bytes_read = 0;
    for (auto& iovec : TRY(copy_typed_array(configuration, iovs, iovs_len))) {
        auto slice = TRY(slice_typed_memory(configuration, iovec.buf, iovec.buf_len));
        auto result = read(fd_value, slice.data(), slice.size());
        if (result < 0)
            return errno_value_from_errno(errno);
        bytes_read += static_cast<Size>(result);
    }
    return bytes_read;
}

ErrorOr<Result<FDStat>> Implementation::impl$fd_fdstat_get(Configuration&, FD fd)
{
    auto mapped_fd = map_fd(fd);
    auto resolved_fd = -1;
    mapped_fd.visit(
        [&](PreopenedDirectoryDescriptor descriptor) {
            auto& entry = preopened_directories()[descriptor.value()];
            resolved_fd = entry.opened_fd.value_or_lazy_evaluated([&] {
                ByteString path = entry.host_path.string();
                return open(path.characters(), O_DIRECTORY, 0);
            });
            entry.opened_fd = resolved_fd;
        },
        [&](u32 fd) {
            resolved_fd = fd;
        },
        [](UnmappedDescriptor) {});
    if (resolved_fd < 0)
        return errno_value_from_errno(errno);

    struct stat stat_buf;
    if (fstat(resolved_fd, &stat_buf) < 0)
        return errno_value_from_errno(errno);

    return FDStat {
        .fs_filetype = file_type_of(stat_buf),
        .fs_flags = fd_flags_of(stat_buf),
        .fs_rights_base = Rights { .data = 0 },
        .fs_rights_inheriting = Rights { .data = 0 },
    };
}

ErrorOr<Result<FileSize>> Implementation::impl$fd_seek(Configuration&, FD fd, FileDelta offset, Whence whence)
{
    auto mapped_fd = map_fd(fd);
    if (!mapped_fd.has<u32>())
        return errno_value_from_errno(EBADF);

    u32 fd_value = mapped_fd.get<u32>();
    auto result = lseek(fd_value, offset, static_cast<int>(whence));
    if (result < 0)
        return errno_value_from_errno(errno);
    return FileSize(result);
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"

ErrorOr<Result<Timestamp>> Implementation::impl$clock_res_get(Configuration&, ClockID id)
{
    return Errno::NoSys;
}
ErrorOr<Result<void>> Implementation::impl$fd_advise(Configuration&, FD, FileSize offset, FileSize len, Advice) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_allocate(Configuration&, FD, FileSize offset, FileSize len) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_datasync(Configuration&, FD) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_fdstat_set_flags(Configuration&, FD, FDFlags) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_fdstat_set_rights(Configuration&, FD, Rights fs_rights_base, Rights fs_rights_inheriting) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_filestat_set_size(Configuration&, FD, FileSize) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_filestat_set_times(Configuration&, FD, Timestamp atim, Timestamp mtim, FSTFlags) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$fd_pread(Configuration&, FD, Pointer<IOVec> iovs, Size iovs_len, FileSize offset) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$fd_pwrite(Configuration&, FD, Pointer<CIOVec> iovs, Size iovs_len, FileSize offset) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$fd_readdir(Configuration&, FD, Pointer<u8> buf, Size buf_len, DirCookie cookie) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_renumber(Configuration&, FD from, FD to) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$fd_sync(Configuration&, FD) { return Errno::NoSys; }
ErrorOr<Result<FileSize>> Implementation::impl$fd_tell(Configuration&, FD) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_filestat_set_times(Configuration&, FD, LookupFlags, Pointer<u8> path, Size path_len, Timestamp atim, Timestamp mtim, FSTFlags) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_link(Configuration&, FD, LookupFlags, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$path_readlink(Configuration&, FD, LookupFlags, Pointer<u8> path, Size path_len, Pointer<u8> buf, Size buf_len) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_remove_directory(Configuration&, FD, Pointer<u8> path, Size path_len) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_rename(Configuration&, FD, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_symlink(Configuration&, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$path_unlink_file(Configuration&, FD, Pointer<u8> path, Size path_len) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$poll_oneoff(Configuration&, ConstPointer<Subscription> in, Pointer<Event> out, Size nsubscriptions) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$proc_raise(Configuration&, Signal) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$sched_yield(Configuration&) { return Errno::NoSys; }
ErrorOr<Result<FD>> Implementation::impl$sock_accept(Configuration&, FD fd, FDFlags fd_flags) { return Errno::NoSys; }
ErrorOr<Result<SockRecvResult>> Implementation::impl$sock_recv(Configuration&, FD fd, Pointer<IOVec> ri_data, Size ri_data_len, RIFlags ri_flags) { return Errno::NoSys; }
ErrorOr<Result<Size>> Implementation::impl$sock_send(Configuration&, FD fd, Pointer<CIOVec> si_data, Size si_data_len, SIFlags si_flags) { return Errno::NoSys; }
ErrorOr<Result<void>> Implementation::impl$sock_shutdown(Configuration&, FD fd, SDFlags how) { return Errno::NoSys; }

#pragma GCC diagnostic pop

template<size_t N>
static Array<Bytes, N> address_spans(Span<Value> values, Configuration& configuration)
{
    Array<Bytes, N> result;
    auto memory = configuration.store().get(MemoryAddress { 0 })->data().span();
    for (size_t i = 0; i < N; ++i)
        result[i] = memory.slice(values[i].to<i32>());
    return result;
}

#define ENUMERATE_FUNCTION_NAMES(M) \
    M(args_get)                     \
    M(args_sizes_get)               \
    M(environ_get)                  \
    M(environ_sizes_get)            \
    M(clock_res_get)                \
    M(clock_time_get)               \
    M(fd_advise)                    \
    M(fd_allocate)                  \
    M(fd_close)                     \
    M(fd_datasync)                  \
    M(fd_fdstat_get)                \
    M(fd_fdstat_set_flags)          \
    M(fd_fdstat_set_rights)         \
    M(fd_filestat_get)              \
    M(fd_filestat_set_size)         \
    M(fd_filestat_set_times)        \
    M(fd_pread)                     \
    M(fd_prestat_get)               \
    M(fd_prestat_dir_name)          \
    M(fd_pwrite)                    \
    M(fd_read)                      \
    M(fd_readdir)                   \
    M(fd_renumber)                  \
    M(fd_seek)                      \
    M(fd_sync)                      \
    M(fd_tell)                      \
    M(fd_write)                     \
    M(path_create_directory)        \
    M(path_filestat_get)            \
    M(path_filestat_set_times)      \
    M(path_link)                    \
    M(path_open)                    \
    M(path_readlink)                \
    M(path_remove_directory)        \
    M(path_rename)                  \
    M(path_symlink)                 \
    M(path_unlink_file)             \
    M(poll_oneoff)                  \
    M(proc_exit)                    \
    M(proc_raise)                   \
    M(sched_yield)                  \
    M(random_get)                   \
    M(sock_accept)                  \
    M(sock_recv)                    \
    M(sock_send)                    \
    M(sock_shutdown)

struct Names {
#define NAME(x) FlyString x;
    ENUMERATE_FUNCTION_NAMES(NAME)
#undef NAME

    static ErrorOr<Names> construct()
    {
        return Names {
#define NAME(x) .x = TRY(FlyString::from_utf8(#x##sv)),
            ENUMERATE_FUNCTION_NAMES(NAME)
#undef NAME
        };
    }
};

ErrorOr<HostFunction> Implementation::function_by_name(StringView name)
{
    auto name_for_comparison = TRY(FlyString::from_utf8(name));
    static auto names = TRY(Names::construct());

#define IMPL(x)                         \
    if (name_for_comparison == names.x) \
        return invocation_of<&Implementation::impl$##x>(#x##sv);

    ENUMERATE_FUNCTION_NAMES(IMPL)

#undef IMPL

    return Error::from_string_literal("No such host function");
}

namespace ABI {

template<typename T>
struct HostTypeImpl {
    using Type = T;
};

template<Enum T>
struct HostTypeImpl<T> {
    using Type = UnderlyingType<T>;
};

template<typename T>
struct HostTypeImpl<LittleEndian<T>> {
    using Type = typename HostTypeImpl<T>::Type;
};

template<typename T, typename t, typename... Fs>
struct HostTypeImpl<DistinctNumeric<T, t, Fs...>> {
    using Type = typename HostTypeImpl<T>::Type;
};

template<typename T>
using HostType = typename HostTypeImpl<T>::Type;

template<typename T>
auto CompatibleValueType = IsOneOf<HostType<T>, char, i8, i16, i32, u8, u16>
    ? Wasm::ValueType(Wasm::ValueType::I32)
    : Wasm::ValueType(Wasm::ValueType::I64);

template<typename RV, typename... Args, ErrorOr<RV> (Implementation::*impl)(Configuration&, Args...)>
struct InvocationOf<impl> {
    HostFunction operator()(Implementation& self, StringView function_name)
    {
        using R = typename decltype([] {
            if constexpr (IsSame<RV, Result<void>>)
                return TypeWrapper<void> {};
            else if constexpr (IsSpecializationOf<RV, Result>)
                return TypeWrapper<RemoveCVReference<decltype(*declval<RV>().result())>> {};
            else
                return TypeWrapper<RV> {};
        }())::Type;

        Vector<ValueType> arguments_types { CompatibleValueType<typename ABI::ToCompatibleValue<Args>::Type>... };
        if constexpr (!IsVoid<R>) {
            if constexpr (requires { declval<typename R::SerializationComponents>(); }) {
                for_each_type<typename R::SerializationComponents>([&]<typename T>(TypeWrapper<T>) {
                    arguments_types.append(CompatibleValueType<typename ABI::ToCompatibleValue<Pointer<T>>::Type>);
                });
            } else {
                arguments_types.append(CompatibleValueType<typename ABI::ToCompatibleValue<Pointer<R>>::Type>);
            }
        }

        Vector<ValueType> return_ty;
        if constexpr (IsSpecializationOf<RV, Result>)
            return_ty.append(ValueType(ValueType::I32));

        return HostFunction(
            [&self, function_name](Configuration& configuration, Vector<Value>& arguments) -> Wasm::Result {
                Tuple args = [&]<typename... Ts, auto... Is>(IndexSequence<Is...>) {
                    return Tuple { ABI::deserialize(ABI::to_compatible_value<Ts>(arguments[Is]))... };
                }.template operator()<Args...>(MakeIndexSequence<sizeof...(Args)>());

                auto result = args.apply_as_args([&](auto&&... impl_args) { return (self.*impl)(configuration, impl_args...); });
                dbgln_if(WASI_DEBUG, "WASI: {}({}) = {}", function_name, arguments, result);
                if (result.is_error()) {
                    auto error = result.release_error();
                    if (error.is_errno())
                        return Wasm::Trap { ByteString::formatted("exit:{}", error.code() + 1) };
                    return Wasm::Trap { ByteString::formatted("Invalid call to {}() = {}", function_name, error) };
                }

                auto value = result.release_value();
                if constexpr (IsSpecializationOf<RV, Result>) {
                    if (value.is_error())
                        return Wasm::Result { Vector { Value { static_cast<u32>(to_underlying(value.error().value())) } } };
                }

                if constexpr (!IsVoid<R>) {
                    // Return values are passed as pointers, after the arguments
                    if constexpr (requires { &R::serialize_into; }) {
                        constexpr auto ResultCount = []<auto N>(void (R::*)(Array<Bytes, N>) const) { return N; }(&R::serialize_into);
                        ABI::serialize(*value.result(), address_spans<ResultCount>(arguments.span().slice(sizeof...(Args)), configuration));
                    } else {
                        ABI::serialize(*value.result(), address_spans<1>(arguments.span().slice(sizeof...(Args)), configuration));
                    }
                }
                // Return value is errno, we have nothing to return.
                return Wasm::Result { Vector<Value> { Value(ValueType(ValueType::Kind::I32)) } };
            },
            FunctionType {
                move(arguments_types),
                return_ty,
            },
            function_name);
    }
};

};

Errno errno_value_from_errno(int value)
{
    switch (value) {
#ifdef ESUCCESS
    case ESUCCESS:
        return Errno::Success;
#endif
    case E2BIG:
        return Errno::TooBig;
    case EACCES:
        return Errno::Access;
    case EADDRINUSE:
        return Errno::AddressInUse;
    case EADDRNOTAVAIL:
        return Errno::AddressNotAvailable;
    case EAFNOSUPPORT:
        return Errno::AFNotSupported;
    case EAGAIN:
        return Errno::Again;
    case EALREADY:
        return Errno::Already;
    case EBADF:
        return Errno::BadF;
    case EBUSY:
        return Errno::Busy;
    case ECANCELED:
        return Errno::Canceled;
    case ECHILD:
        return Errno::Child;
    case ECONNABORTED:
        return Errno::ConnectionAborted;
    case ECONNREFUSED:
        return Errno::ConnectionRefused;
    case ECONNRESET:
        return Errno::ConnectionReset;
    case EDEADLK:
        return Errno::Deadlock;
    case EDESTADDRREQ:
        return Errno::DestinationAddressRequired;
    case EDOM:
        return Errno::Domain;
    case EEXIST:
        return Errno::Exist;
    case EFAULT:
        return Errno::Fault;
    case EFBIG:
        return Errno::FBig;
    case EHOSTUNREACH:
        return Errno::HostUnreachable;
    case EILSEQ:
        return Errno::IllegalSequence;
    case EINPROGRESS:
        return Errno::InProgress;
    case EINTR:
        return Errno::Interrupted;
    case EINVAL:
        return Errno::Invalid;
    case EIO:
        return Errno::IO;
    case EISCONN:
        return Errno::IsConnected;
    case EISDIR:
        return Errno::IsDirectory;
    case ELOOP:
        return Errno::Loop;
    case EMFILE:
        return Errno::MFile;
    case EMLINK:
        return Errno::MLink;
    case EMSGSIZE:
        return Errno::MessageSize;
    case ENAMETOOLONG:
        return Errno::NameTooLong;
    case ENETDOWN:
        return Errno::NetworkDown;
    case ENETRESET:
        return Errno::NetworkReset;
    case ENETUNREACH:
        return Errno::NetworkUnreachable;
    case ENFILE:
        return Errno::NFile;
    case ENOBUFS:
        return Errno::NoBufferSpace;
    case ENODEV:
        return Errno::NoDevice;
    case ENOENT:
        return Errno::NoEntry;
    case ENOEXEC:
        return Errno::NoExec;
    case ENOLCK:
        return Errno::NoLock;
    case ENOMEM:
        return Errno::NoMemory;
    case ENOPROTOOPT:
        return Errno::NoProtocolOption;
    case ENOSPC:
        return Errno::NoSpace;
    case ENOSYS:
        return Errno::NoSys;
    case ENOTCONN:
        return Errno::NotConnected;
    case ENOTDIR:
        return Errno::NotDirectory;
    case ENOTEMPTY:
        return Errno::NotEmpty;
    case ENOTRECOVERABLE:
        return Errno::NotRecoverable;
    case ENOTSOCK:
        return Errno::NotSocket;
    case ENOTSUP:
        return Errno::NotSupported;
    case ENOTTY:
        return Errno::NoTTY;
    case ENXIO:
        return Errno::NXIO;
    case EOVERFLOW:
        return Errno::Overflow;
    case EPERM:
        return Errno::Permission;
    case EPIPE:
        return Errno::Pipe;
    case EPROTO:
        return Errno::Protocol;
    case EPROTONOSUPPORT:
        return Errno::ProtocolNotSupported;
    case EPROTOTYPE:
        return Errno::ProtocolType;
    case ERANGE:
        return Errno::Range;
    case ESPIPE:
        return Errno::SPipe;
    case ESRCH:
        return Errno::SRCH;
    case ESTALE:
        return Errno::Stale;
    case ETIMEDOUT:
        return Errno::TimedOut;
    case ETXTBSY:
        return Errno::TextBusy;
    case EXDEV:
        return Errno::XDev;
    default:
        return Errno::Invalid;
    }
}

FileType file_type_of(struct stat const& buf)
{
    switch (buf.st_mode & S_IFMT) {
    case S_IFDIR:
        return FileType::Directory;
    case S_IFCHR:
        return FileType::CharacterDevice;
    case S_IFBLK:
        return FileType::BlockDevice;
    case S_IFREG:
        return FileType::RegularFile;
    case S_IFIFO:
        return FileType::Unknown; // FIXME: FileType::Pipe is currently not present in WASI (but it should be) so we use Unknown for now.
    case S_IFLNK:
        return FileType::SymbolicLink;
    case S_IFSOCK:
        return FileType::SocketStream;
    default:
        return FileType::Unknown;
    }
}
FDFlags fd_flags_of(struct stat const&)
{
    FDFlags::Bits result {};
    return FDFlags { result };
}
}

namespace AK {
template<>
struct Formatter<Wasm::Wasi::Errno> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::Errno const& value)
    {
        return Formatter<FormatString>::format(builder, "{}"sv, to_underlying(value));
    }
};

template<>
struct Formatter<Empty> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder&, Empty)
    {
        return {};
    }
};

template<typename T>
struct Formatter<Wasm::Wasi::Result<T>> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::Result<T> const& value)
    {
        if (value.is_error())
            return Formatter<FormatString>::format(builder, "Error({})"sv, *value.error());

        return Formatter<FormatString>::format(builder, "Ok({})"sv, *value.result());
    }
};

template<OneOf<Wasm::Wasi::ArgsSizes, Wasm::Wasi::EnvironSizes> T>
struct Formatter<T> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, T const& value)
    {
        return Formatter<FormatString>::format(builder, "size={}, count={}"sv, value.size, value.count);
    }
};

template<>
struct Formatter<Wasm::Wasi::FDStat> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::FDStat const&)
    {
        return Formatter<FormatString>::format(builder, "(rights)"sv);
    }
};

template<>
struct Formatter<Wasm::Wasi::FileStat> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::FileStat const& value)
    {
        return Formatter<FormatString>::format(builder, "dev={}, ino={}, ft={}, nlink={}, size={}, atim={}, mtim={}, ctim={}"sv,
            value.dev, value.ino, to_underlying(value.filetype), value.nlink, value.size, value.atim, value.mtim, value.ctim);
    }
};

template<>
struct Formatter<Wasm::Wasi::PreStat> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::PreStat const& value)
    {
        return Formatter<FormatString>::format(builder, "length={}"sv, value.dir.pr_name_len);
    }
};

template<>
struct Formatter<Wasm::Wasi::SockRecvResult> : AK::Formatter<FormatString> {
    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::SockRecvResult const& value)
    {
        return Formatter<FormatString>::format(builder, "size={}"sv, value.size);
    }
};
}